1. Field of the Invention
This invention relates to a power window apparatus for automobiles and, more particularly, to an automatic window glass elevating apparatus for automatically controlling the elevation of a window glass for a vehicle by detecting the variation in a loading state of a driving motor (hereinafter referred to as "a motor") for opening or closing the window glass.
2. DESCRIPTION OF THE PRIOR ART
In a conventional power window apparatus, a reversible motor for moving a window glass upward in a closing direction and downward in an opening direction is held energized upward or downward by the one-touch operation of a switch. The power window apparatus of this type has an automatic circuit and a switch for automatically moving the window glass upward or downward. When the window glass is in a locked state due to a foreign material interposed between the window glass and a window frame as the window glass is contacted with the window frame in the case that the window glass is moved upward or as the window glass is further moved upward in the case that the window glass arrives at the lower limit, a driving current flowing in the motor increases excessively. Then, detecting means for judging whether the driving current exceeds a reference value or not is provided in the power window apparatus to stop or reversely move the motor by the detection signal of the detecting means.
In such a conventional power window apparatus, a driving current flowing in the motor when the window glass is normally moved upward or downward is largely affected by the influence of the mismatch of the window frame and the window glass or a variation in the terminal voltage of an automotive storage battery as a power source to become remarkably irregular. Thus, the reference value for judging the locking state must be set high.
When the reference value for judging the locking state is high, a large load is applied to the motor when judging the locking state, and it is dangerous because a large holding force is produced between the window glass and the window frame when an arm, fingers or a neck of a human body is interposed partly between the window glass and the window frame. Further, whenever the window glass arrives at the upward or downward limit, a large driving current repeatedly flows in the motor. As a result, there arise drawbacks that the nominal life of the motor is considerably shortened and an automotive storage battery which is the power source may be overdischarged.
FIG. 6 is a waveform diagram of a current in the motor from the start of the motor to the lock of the motor. In FIG. 6, a curve in a starting range (1) indicates the current at the starting time, a curve in an ordinary range (2) indicates the current at the ordinary time, and a curve in a motor lock range (3) is the current at the locking time.
As shown in FIG. 6, the motor current has characteristics that the current is higher at the starting and locking times than during the ordinary range time.
When the starting range (1) can be ignored, the time point when the motor current abruptly rises is judged as the locking state of the motor by utilizing the characteristics of the motor current so as to interrupt the current to the motor.
Since the abrupt rise of the motor current is ignored in the starting range (1) described above, the following method can be employed.
FIG. 7 is a waveform diagram for explaining a method for ignoring the abrupt rise of the motor current in the starting range, where reference character A designates a waveform curve of the motor current converted to a voltage, delayed at t seconds according to the voltage and further added with a value a, and reference character B denotes a waveform curve of the motor current converted to a voltage, and cancelled at the waveform portion (designated by a broken line) at the starting time.
In FIG. 7, a point C where the waveform curve A and the waveform curve B cross is used for the detection of the motor locking time. According to this method, even when the motor current varies due to an irregularity in the characteristics of the motor or a variation in the environment, such as an environmental temperature, the locking time of the motor can be always detected correctly as long as the relationship "locking current larger than ordinary current" is satisfied.
The conventional automatic window glass elevating apparatus of this type is also disclosed in Japanese Patent Laid-open Nos. 39873/1986 and 49086/1986.
In the above-mentioned prior art, when the window glass is located at the uppermost or lowermost position, or at the holding position described above, the abrupt rise of the motor current is detected to stop the motor, but when an automatic circuit for automatically moving the window glass downward as the window glass is disposed at the lowermost position is operated, i.e., when the motor immediately enters a locking state from the starting time, the absolute value of the current flowing in the motor is detected to release the automatic operation if it continues for a predetermined time.
However, according to this method, it has such disadvantages that the predetermined time is required to release the automatic operation and the current continuously flows without releasing the automatic operation according to the characteristic irregularity of the motor causing the motor to be overheated.